Sally Bercow, the wife of the Commons Speaker, yesterday described the Tory leader, David Cameron, as a "merchant of spin", baiting traditionalists who believe she is politicising her husband's apolitical office.

She recently declared her intention to run as a Labour council candidate and has made no secret of the fact that her political leanings differ from that of her husband, John Bercow, the Conservative MP for Buckingham. He however has gravitated from the right of his party to the left, with many continually predicting a defection to Labour.

Yesterday, in an interview with the Evening Standard, Sally Bercow made her feelings about Cameron plain, saying: "He's just a merchant of spin. I think he's really an archetypal Tory. He favours the interests of the few over the mainstream majority. Deep down, I do think the Tory party is for the privileged few, and what it stands for isn't in the interests of most ordinary people. They're not really interested in opportunity for all.

"He has his children at state school now, but let's see what happens at secondary level. There's not a real commitment to the state sector among the Tories. The vast majority of the shadow cabinet send their children privately."

She might also complicate matters for her husband with his constituency, since she criticised grammar schools, of which there are many in Buckingham. She said: "I don't even want to send the children to the grammars in John's constituency. I'm strongly against selection, because it entrenches privilege."

A growing number of purists suggest that her husband's position as Commons Speaker would be untenable if she became a Labour MP. The Speaker is meant to assume impartiality and John Bercow's election to that post was only successful because he received the support of a large number of Labour MPs.

His wife used the interview as a confessional ahead of her attempt to become a Labour councillor: she admitted to casual sex in her 20s and binge drinking. She has been a teetotaller since 2000.

The Conservative MP Nadine Dorries, a critic of John Bercow, said: "We desperately need to restore both authority and respect to parliament. What this interview has done is remove any painstaking progress parliament has made and reduced the Speaker and his office to that of a laughing stock."